The invention relates to a method for control of engine torque during automated gear changing in mechanical stepped gearboxes.
During automatic gear changing in mechanical stepped gearboxes, an adjustment of the torque delivered by the engine is required in order to reduce the torque transmitted by the current gear combination.
In cases where a clutch servo is incorporated and there is automatic disengagement of the disc clutch, which is conventionally situated between the engine and the gearbox, the torque load which the engine imposes on the gear combination is removed automatically. In such cases the primary purpose of engine torque reduction, which is achieved by reducing the fuel quantity, is to prevent the engine racing when the clutch breaks the connection between the engine and the gearbox. This means that the torque levels down to which the engine is adjusted in connection with disengaging the gear become less critical. Such a gear change system with clutch servo and fuel reduction in connection with gear disengagement is applied in U.S. Pat. No. 5,136,897, in which thereafter, when the next higher gear is engaged, the engine acceleration caused by subsequent fuel boost is detected with a view to ordering re-engagement of the disc clutch so that the latter re-engages at the same time as the synchronous speed calculated on the basis of the engine acceleration is reached and the gear is engaged.
Another solution for making it easy in the higher gears to change up without disengaging the disc clutch is described in U.S. Pat. No. 4,850,236, which applies a method whereby the gear disengagement servo is ordered to disengage the gear, after which the torque is adjusted so that a transmitted positive torque forcibly modulated from the engine with increased fuel quantity changes to a torque reduction by reduction of the fuel quantity, which reduction proceeds until the transmitted torque in the current gear combination changes to a negative torque, thereby resulting in zero torque taking place during simultaneous action of the gear disengagement servo. A disengaging force may thus be exerted on the gear, which springs out when this zero-torque transition takes place. This method may be sufficient for achieving gear changes without disc clutch disengagement between higher gears, since the requirement for precise engine adjustment is not as manifest as during automatic gear change without disengagement between lower gears. This solution does mean, however, that during the torque adjustment the gear disengagement servo acts on the gear combination in a disengaging direction, which may cause bangs when the gear combination disengages if the disengaging force is great enough for disengagement to take place before the zero-torque level is reached. This method may also result in increased wear on gearwheels.